I haven't felt the need to adjust my settings, but you can change the sensitivity in Mame which may help. I'm sure there is a way to set this globally, but I'm not sure how - except to edit the default.cfg file. But, here's how you can change in at least one game to see if this can help:
Fire up a game in Mame. Hit Tab. Go to Analog controls. Adjust your Trackball X and Y sensitivity, (higher is more sensitive), try the game, and see if it's any better. Perhaps someone else can help with how to set globally, if that works...